1. Field of the Invention
The invention relates to a measuring device having at least one housing and at least two electronic units.
2. Description of Related Art
Occasionally, so-called construction kits or modular systems are used for the implementation of a wide range of different measuring devices with respect to measurement principles and also to dimensions or prevention classes, etc. In this case, the concerned measuring devices are similarly constructed and assembled from interchangeable components as far as is possible. This has the advantage, on the one hand, of a uniform appearance having a recognition value. On the other hand, this reduces the cost of manufacturing or, respectively provides greater flexibility to adapt to specific requirements of the measuring devices. For this, the measuring devices are mostly divided into individual components that can be combined with each other, which can, in turn, be constructed in a modular manner.
For measuring devices, there is a possible separation between sensor units, in which the measurement principle for the actual measurement of the process variable is implemented, and electronic units, which evaluate or process the raw data or measurement data that the sensor unit generates. Here, the sensor unit can also have its own electronic components used in measurement or, respectively the removal or conversion of raw data. Both the sensor and the electronic unit are usually arranged in a respective housing, wherein the housing of the sensor unit has, where applicable, an opening for direct contact with the measurement medium to be measured and the housing of the electronic unit has at least one opening for power supply or transmission of measured values, for example, to a higher-level unit. Furthermore, the two housings are usually designed in such a manner, that they can be connected with each other and that also energy or signals can be transmitted between the sensor and the electronic unit.
An electronic unit can be further divided into several modules that are possibly even arbitrarily interchangeable or combinable. Partitions are possible in a central unit, which are used for energy supply, for the control system, for the measurement and the processing of signals from the sensor unit into output signals, in a connecting or converting unit, for connecting the measuring device and, in the case of a display or control unit, for displaying the measured value or, respectively for operating the measuring device on site.
Depending on the degree of modularization, any ports for different bus systems can be combined with any display units and different types of sensors. A modular design of the electronic unit is shown for example, in the published German Patent Application DE 10 2006 009 827 A1 and corresponding to U.S. Pat. No. 7,894,175 B2 or German Patent Application DE 10 2009 054 649 A1 or German Patent Application DE 197 82 057 B4 which corresponds to U.S. Pat. No. 5,954,526. The German Patent Application DE 101 26 654 A1 discloses a housing for a measuring device with a display and a separate port space for the inclusion of a display or of a connecting module. A similar structure is disclosed in the European Patent EP 0 775 292 B1 and corresponding U.S. Pat. No. 5,546,804 having a housing with two separate chambers separated by a wall with an opening. The electronic components in the chambers are in contact with one another via signal pins that are molded in the opening. In the German Utility Model DE 203 14 618 U1, a pin casting is encapsulated within a passageway between two compartments of the housing. Another design of a housing and the modular electronic components located therein is described in International Patent Application Publication WO 2011/160949 A1. Plug contacts in a cast measuring device that connect directly to an electronic component and that are used for connection to other electronic elements are disclosed, for example, in German Patent Application DE 102 33 296 A1.
In many applications, intrinsic safety is required by the measuring devices. The ignition protection designation “intrinsically safe” is mainly based on a limitation of the electrical energy within the electronics of the measuring device or within sections of it and the electric energy of connecting lines to a level below the level at which contact with a potentially explosive atmosphere can cause ignition. An essential requirement resulting from relevant standards is the compliance of separation distances between conductive components. The separation distance is the shortest distance between two such components. A distinction is made according to the nature of the medium through which the route of the shortest distance leads, so that different separation distances result for clearance, distances in casting, distances through solid insulation, creepage distances in air or creepage distances under a protective layer. In addition, the separation distances to be observed are dependent on the maximum voltages occurring between the conductive components.
Details for designing modular electronic components and their housings for a possible use in a modular system for measuring devices are also found in the prior art. Thus, German Patent Application DE 10 2010 033 470 A1 and corresponding U.S. Patent Application Publication 2012/0032822 A1 describes an operating panel for the measuring devices and German Patent Application DE 41 09 475 A1 describes a rotatable display. A rotatable mechanical connection between the sensor unit and the housing of the electronic unit is shown in the German Patent Application DE 10 2004 044 890 A1 . An exchangeable connection between the sensor unit via a type of plug having a field bus or alternatively having a programming device can be seen in German Patent Application DE 103 27 013 A1. Further details, such as the easier insertion of a cable into a housing (e.g., German Patent DE 10 2007 036 484 B3 and corresponding U.S. Patent Application Publication 2010/0208769 A1), producing a hard metal threading inside an aluminum housing (e.g., U.S. Pat. No. 3,462,539), the surrounding of lead wires in a device with ceramic or glass casings (e.g., German Utility Model DE 20 2010 007 043 U1), the fixing of electronic components via conical slopes in the housing (e.g., German Patent Application DE 10 2005 024 259 A1) or special devices on the outside of the housing for seals (e.g., German Patent Application DE 10 2010 003 743 A1) can also been found in the prior art and can contribute to the design of the measuring devices and their housings.